The present invention relates to a developing solution and a method for developing an exposed photographic silver halide material.
It is known that by processing a silver halide photographic material finely divided metallic silver, so-called silver deposit, is formed in the developer (ref. e.g. Photographic Silver Halide Diffusion Processes by A. Rott and E. Weydexe2x80x94The Focal Press, (1972), p. 67). The formation of silver deposit is particularly disturbing in automatic processing apparatus wherein it results in deposits of black silver on conveyor and transport rollers and smudging of photographic material conducted therewith.
The formation of silver deposit can be attributed to the presence in conventional developers of silver halide complexing agents like, e.g., sulphite and thiocyanate ions, which are present for stability and speed. In this medium the complex ions formed are effectively reduced to metallic silver nuclei. Growth of said nearly invisible fine nuclei leads to the formation of said silver deposit. As a consequence regularly cleaning of the automatic processing machines is required. When a film is introduced into the processor as first film of a whole series of films, its first contact with the first stained roller releases the deposit from the said roller or disturbs the deposited layer. As a consequence after one rotation of the said roller the unevenly distributed dirt or stain comes into contact again with the transported film surface so that it may be deposited onto said surface. This phenomenon is recurrently repeated, not only at the first roller, but also at the further rollers that are mounted onto the racks and is well-known as xe2x80x9cpi-linexe2x80x9d defect. The crystalline silver deposit may further cause damaging of the surface of the coated hydrophilic layers on the film and/or cause locally situated pressure phenomena, resulting in xe2x80x9cartefactsxe2x80x9d, thereby seriously impeding the diagnostic value of the obtained image. Especially when the silver halide photographic material shows processed images with a diagnostic value, like, e.g., in medical imaging or in non-destructive testing, said diagnostic value may be impaired.
Besides the occurrence of this defect in processed materials for radiographic recording and duplicating, it can also be detected at films and papers for general amateur and professional photography, at materials for pre-press graphic arts applications, films for cinematographic recording and printing, materials which after processing can serve as planographic printing plates, microfilm applications, etc.
In order to prevent the formation of silver deposit it has been proposed to add particular compounds to the developer, forming sparingly soluble and non-reducible silver salts, as, e.g., 5,5xe2x80x2-bis-1,2,4-triazoline-3-thiones or derivatives of 1,3,4-thiadiazole-2-thiols as described, e.g. in BE-P 606,550 and GB-P 1,120,963, 2-mercapto-1,3,4-thiadiazoles described in U.S. Pat. No. 3,212,892. A great variety of other mercapto compounds has been described in FR-P 1,470,235 and 1-phenyl-5-mercapto-tetrazole compounds having a xe2x80x94NHX substituent on the phenyl nucleus have been disclosed in GB-P 1,471,554. In the latter document it has been described that the emulsion layer may contain auxiliary coating agents such as saponin, sodium lauryl sulphate, dodecylphenol polyethylene oxide ether and hexadecyltrimethyl ammonium bromide.
The same result can be obtained by the presence in the developer of the fog inhibitor 1-phenyl-5-mercaptotetrazole, but if it is used in an amount higher than necessary for reducing fog in the silver halide photographic material, the sensitivity of the said material is markedly reduced. Such effect is probably due to the penetrating of the 1-phenyl-5-mercaptotetrazole from the developer liquid into the exposed photographic silver halide emulsion layer and its interaction with latent image nuclei. More recently triazolium thiolates for use in the developer have been described in e.g. EP-A 0 533 182.
In EP-Specification 0 223 883 a method to reduce the appearance of silver deposit has been described which comprises the treating of a silver halide photographic material with an aqueous alkaline liquid in the presence of (i) a developing agent, (ii) a heterocyclic mercapto compound including an aliphatic group of at least 3 carbon atoms and (iii) a surface active agent, characterised in that said surface active agent is an anionic alkylphenoxy polyalkyleneoxy phosphate ester surfactant.
In EP-A 0 620 484, reduction of the so-called xe2x80x9cpi-linexe2x80x9d defect, already mentioned hereinbefore, especially for processed materials for non-destructive testing purposes, has been described. Such materials should comprise at least one vinyl sulphone compound as a hardening agent and at least one polyoxyalkylene compound as a surfactant in at least one of its hydrophilic layers. Combined with a processing method comprising a developing step wherein the developer comprises as a surfactant at least one anionic alkylphenoxy and/or alkoxy polyalkyleneoxy phosphate ester, sulphate ester, alkyl carboxylic, sulphonic or phosphonic acid and/or a salt thereof a remarkable improvement has been obtained. A similar result has been obtained as disclosed in EP-A""s 0 621 506 and 0 620 483.
Although said methods to reduce the amount of silver deposit are very effective it is not more than a xe2x80x9ctreating methodxe2x80x9d wherein the amount of silver nuclei is not decreased but wherein said nuclei are more xe2x80x9cdispersedxe2x80x9d and are merely inhibited to grow further to form larger crystalline silver deposits. No xe2x80x9ccuringxe2x80x9d effect in the sense of reducing the generation of nuclei can be obtained with these methods. Moreover the stability of the developer, especially its sensitivity to oxidation by contact with air oxygen, is not improved either.
It is an object of the present invention to provide a stable developer and a method for developing a photographic silver halide material wherein the formation of silver deposit is reduced effectively without adversely affecting photographic speed.
It is a further object of the present invention to provide a suitable sensitometry for the material processed in the developer used according to the method of this invention.
Moreover it is an object to provide a developing method, wherein the developer is stable against oxidation by air oxygen as a low regeneration volume per square unit of the said material should be highly appreciated.
Other objects and advantages of the present invention will become clear from the further description.
It has surprisingly been found now that the objects of the invention can be attained by providing a developer having a low pH value between 9.6 and 11.0, preferably between 9.6 and 10.3, and comprising hydroquinone in an amount from 0 to less than 30 g per liter, an auxiliary developing agent, and as silver halide complexing agents alkali metal sulphite salts, preferably sodium salts, in an amount from 0 to less than 50 g per liter, more preferably to less than 40 g per liter, and thiocyanate salts in amounts from 0.1 to 3 g, more preferably from 0.5 to 2.5 g per liter,
and at least 1 g per liter of a compound corresponding to the formula (I), a precursor thereof, a derivative thereof and/or a metal salt thereof 
wherein
each of A, B and D independently represents an oxygen atom or NR1;
X represents an oxygen atom, a sulphur atom, NR2; CR3R4; Cxe2x95x90O; Cxe2x95x90NR5 or Cxe2x95x90S;
Y represents an oxygen atom, a sulphur atom, NRxe2x80x22; CRxe2x80x23Rxe2x80x24; Cxe2x95x90O; Cxe2x95x90NRxe2x80x25 or Cxe2x95x90S;
Z represents an oxygen atom, a sulphur atom, NRxe2x80x32; CRxe2x80x33Rxe2x80x34; Cxe2x95x90O; Cxe2x95x90NRxe2x80x35 or Cxe2x95x90S;
n equals 0, 1 or 2;
each of R1 to R5, Rxe2x80x21 to Rxe2x80x25 and Rxe2x80x31 to Rxe2x80x35, independently represents hydrogen, subsituted or unsubstituted alkyl, aralkyl, hydroxyalkyl, carboxyalkyl; substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted cycloalkenyl, substituted or unsubstituted aryl or substituted or unsubstituted heterocyclyl; and wherein
R3 and R4, Rxe2x80x23 and Rxe2x80x24, Rxe2x80x33 and Rxe2x80x34, may further form together a ring; and
wherein in the case that Xxe2x95x90CR3R4 and Yxe2x95x90CRxe2x80x23Rxe2x80x24, R3 and Rxe2x80x23 and/or R4 and Rxe2x80x24 may form a ring and wherein in the case that Yxe2x95x90CRxe2x80x23Rxe2x80x24 and Zxe2x95x90CRxe2x80x33Rxe2x80x34 with n=1 or 2, Rxe2x80x23 and Rxe2x80x33 and/or Rxe2x80x24 and Rxe2x80x34 may form a ring.
It has unexpectedly been found that a solution of the problem of silver deposit and stability of a developer containing developing agents and lower amounts of silver complexing compounds like alkali metal sulphite salts, is offered by the addition to the said developer of potassium thiocyanate in an amount from 0.1 to 3 grams and of at least 1 g of a compound corresponding to the formula (I) given above, a precursor thereof, a derivative thereof and/or a metal salt thereof.
In a preferred embodiment in the formula (I) A, B and X each represent an oxygen atom; n=0; Yxe2x95x90CHxe2x80x94(CHOH)mxe2x80x94CH2xe2x80x94R6 wherein m=1,2,3 or 4 and wherein R6 represents OH for m=1; H or OH for m=2,3 or 4. This formula corresponds with (iso)ascorbic acid. As a suitable derivative corresponding to the formula (I), iso-ascorbic acid and 1-ascorbic acid are both preferred.
In another preferred embodiment A and B each represent an oxygen atom; n=0 and X and Y each correspond with C(CH3)2. This formula corresponds with tetramethyl reductic acid.
The compound(s) according to the formula (I) preferably is(are) present in the developer solution in an amount comprised between 1 g and 50 g per liter. Examples of reducing precursor compounds have, e.g., been described in WO""s 94/3834 and 94/16362, which are both incorporated herein by reference.
It is clear that within the context of this invention ascorbic acid is not merely used in the developer as an antioxidant as, e.g., described in WO 93/12463, in JP-A""s 4428673 and 55149936, in GB 1,266,533 and in U.S. Pat. Nos. 3,865,591; 4,756,997 and 4,839,259 and in the literature as, e.g., J. Am. Chem. Soc., 60 (1938), p. 99 and p. 2084; 61 (1939), p. 442; 64 (1942), p. 1561, 65 (1943), p. 1489; 66 (1944), p. 700 and 104 (1982), p. 6273.
An essential feature in accordance with this invention is the presence in the developer of an additional amount of at least 0.1 g to 3 g per liter of potassium thiocyanate as a silver complexing agent. An equivalent amount of a thiocyanate salt, having a cation different from potassium may be added.
The developer liquid may contain any combination of hydroquinone as a developing agent and auxiliary developing agent known for use in the development of exposed photographic silver halide. If hydroquinone is absent the said auxiliary developing agent may still be present. For example as auxiliary developing compounds may be utilized p-methylaminophenol, a 1-phenyl-3-pyrazolidine-1-one, p-phenylenediamine derivatives and the like. Amounts of hydroquinone from 0 to less than 30 g per liter can be present and more preferred lower than 20 g per liter. Preferred amounts of auxiliary developer are present in a concentration range of 0 up to 10 mmoles per liter of developer, said auxiliary developer being preferably a 1-phenyl-3-pyrazolidine-1-one compound.
The developer further comprises silver complexing compound(s) such as alkali metal sulphites, bisulphites, metasulphites or metabisulphites. Preferably it contains an alkali metal sulphite salt, and more preferably sodium sulphite, in an amount from 0 to 50, and more preferably in an amount from 0 to 40 g per liter of developer, which is substantially lower than amounts set forth, e.g., in EP 0 538 947, wherein developer compositions have been described for use in the processing of non-destructive testing materials. The developer solution can be alkalised with alkaline metal hydroxides, phosphates, borates, carbonates and the like. The developer liquid or activator liquid may contain still other ingredients, e.g. metal complexing agents, an anti-fogging agent, e.g. alkali metal bromide, in amounts ranging from 0.01 to 0.4 moles per liter, a benzotriazole, a benzothiazole, a tetrazole, e.g., up to 0.06 g per liter of 1-phenyl-5-mercapto-tetrazole, solvents improving the dissolution of the developing agents, e.g., alcohols, polyethylene glycols and esters thereof and alkanolamines, surface active agents, development retarding or activating compounds, e.g., quaternary ammonium salts, and gelatin hardening agents, e.g., dialdehyde compounds such as glutardialdehyde. Especially the presence of polyethylene glycols having a low molecular weight in the range from 200 to 400 is preferred.
It is further clear the developer according to this invention does not contain thiosulphate ions as is the case, e.g., for monobath compositions having a combined developing and fixation action as is demonstrated, e.g., in U.S. Pat. No. 3,867,151.
Important to note is the pH of the developer solution according to this invention, which is in the range of 9.6 to 11.0, and more preferably in the range of 9.6 to 10.3.
It is remarkable that at those relatively low pH values, if compared with more frequently used alkaline pH values of 12.0 and more, the required sensitometry is still attained, which means that a developer having a composition according to this invention offers enough reactivity to get the required sensitivity for a material that is processed therein within a reasonable processing time.
The present invention thus includes a method for developing, by means of the developer according to this invention, any type of photographic silver halide emulsion layer material, e.g., a graphic art, a micrographic or an X-ray recording material, after image-wise exposing the said material by means of suitable radiation sources, adapted to each application in particular, and immersing it into the said developer.
The development process according to the present invention is advantageously applied in automatic processing equipment, preferably one containing conveyer rollers as described, e.g., in U.S. Pat. Nos. 3,025,779 and 3,545,971, in a time between 5 and 45 seconds at a temperature between 25 and 40xc2x0 C.
Preferably the concentration of the compounds corresponding to the formula (I) and the pH is maintained at a constant value by replenishment with unoxidised developing agent, thereby adding a concentrated alkali hydroxide solution under controlled constant redox potential as has been illustrated in EP-A 0 552 511, which is incorporated herein by reference. This invention allows the use of low regeneration amounts of the developer, having a composition as described hereinbefore: low regeneration amounts of developing solution from 50 to 250 ml/m2 of photographic material are possible and even more preferred from 50 to 150 ml/m2.
silver halide emulsions incorporated in at least one photosensitive layer in a suitable layer arrangement of the said materials which can be processed in a developer according to this invention are composed of silver bromide, silver bromoiodide, silver chloride, silver chlorobromide, silver chloroiodide and silver chlorobromoiodide.
Photosensitive silver halide emulsion layer(s) present in silver halide photographic materials used in the method according to this invention may be of any type or composition used in silver halide photography and may be present in whatever a layer arrangement used in the art of photography.
So black-and-white silver halide films intended to be used for contact exposures form an important class of photographic films. These so-called contact films are used for proper reproduction on one hand and for dry dot-etching on the other hand. In modern pre-press graphic arts these contact materials are designed to be usable for several minutes under roomlight conditions, meaning light containing substantially no UV-light. Accurately reproducing the relative proportions of white and black areas of a dot or line image implicates high contrast and high image density. Contact materials usually are processed in Rapid Access chemistry containing hydroquinone, but they give equal or better results, concerning contrast or image density, in Rapid Access chemistry containing ascorbic acid or ascorbic acid derivatives instead of hydroquinone.